Scaffolding structure

ABSTRACT

A scaffolding structure for mounting to a supporting structure such as a bridge includes a track fixable to the supporting structure, and a frame. The frame and track are movable relative to one another, and the frame is also movable relative to the supporting structure between a first position and a second position. In the first position, the track supports the frame, and the track is supported by the supporting structure, so that when the track is fixed to the supporting structure, the frame can advance along the track and therefore along the supporting structure. In the second position, the frame is supported by the supporting structure and the track is supported by the frame, so that the track can advance along the supporting structure. By alternately advancing the frame and the track, the scaffolding structure can advance along the entire length of the supporting structure.

This application claims the benefit under 35 USC 119(e) of U.S. Provisional Application No. 60/621,057, which was filed on Oct. 25, 2004, and the entire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to scaffolding structures, and particularly to scaffolding structures that are useful for the maintenance and repair of bridges.

BACKGROUND OF THE INVENTION

It is well known that routine maintenance of load-bearing structures such as bridges is necessary to remedy normal deterioration and prevent the structures from becoming unsafe to use. While it has been known to support scaffolding from the upper beams of a bridge so that workers can access the sides of the bridge to carry out maintenance, difficulties remain in advancing the scaffolding along the length of the bridge.

A number of structures have been proposed for use in the repair and maintenance of bridges.

U.S. Pat. No. 4,201,275 describes a method for refurbishing and renovating large span overhead structures such as bridges. Runway beams are suspended from the main ribs of the structure, and working platforms are suspended from the runway beams. The runway beams are displaceable from the main ribs, and the working platforms are displaceable along the runway beams. The overhead structure is treated by alternately advancing the working platforms along the runway beams and the runway beams relative to the structure.

U.S. Pat. No. 5,634,528 describes a workstation that can be advanced across a bridge by using a plurality of slotted box beams. The box beams are temporarily fastened to the bridge girders, and wheeled posts that support scaffolding are received within the box beams. The scaffolding can be rolled along the box beams, and new box beams can be placed down as the scaffolding advances, while those that have been passed over can be taken up and moved forward to a new position.

There remains a need, however, for an improved scaffolding structure for use with supporting structures such as bridges, which does not require the use of multiple track elements to advance to scaffolding structure along the bridge.

SUMMARY OF THE INVENTION

In one aspect, the present invention is directed to a scaffolding structure. The scaffolding structure comprises a frame having two side supports and a cross-member connected between the side supports, and at least two feet, at least one foot supporting each side support. The scaffolding structure further comprises at least two rail assemblies, each rail assembly being selectively securable to a supporting structure having a longitudinal direction. Each rail assembly has a housing shaped to retain a corresponding at least one of the at least two feet therewithin and to permit movement of the track and the at least one foot relative to one another in the longitudinal direction of the supporting structure. The scaffolding structure further comprises a mechanism secured to the frame and adapted to selectively move the frame between a first position wherein the frame is movable relative to the rail assemblies and the supporting structure in the longitudinal direction thereof, and a second position wherein the frame is fixed relative to the supporting structure and the rail assemblies are movable relative to the frame and the supporting structure in the longitudinal direction of the supporting structure when not secured thereto.

Preferably, the first position of the frame is a non-elevated position relative to the supporting structure, and the second position is an elevated position relative to the supporting structure. The mechanism preferably comprises a plurality of jacks, at least one jack being associated with each foot, wherein the jacks are adapted to engage the supporting structure and elevate the frame into the second position.

Each housing has an interior surface or surfaces, and each at least one foot comprises a member or members for rollably engaging the interior surface or surfaces of the corresponding housing within which the foot is retained. Preferably, each housing has an upper interior surface and a lower interior surface, each foot comprises a wheel or wheels, and when the frame is in the first position, the wheel or wheels support the frame and are rollably disposed on the lower interior surface of the corresponding housing, and when the frame is in the second position, each at least one rail assembly is supported by its upper interior surface, the upper interior surface resting rollably on the wheel or wheels of the corresponding foot.

In another aspect, the present invention is directed to a scaffolding structure comprising a frame and a track that is selectively fixable to a supporting structure having a longitudinal direction, the track being movably mountable to the frame. The scaffolding structure further comprises a mechanism secured to the frame and adapted to selectively move the frame between a first position wherein the frame is movable relative to the track and the supporting structure in the longitudinal direction of the supporting structure, and a second position wherein the frame is fixed relative to the supporting structure and the track is movable relative to the frame and the supporting structure in the longitudinal direction of the supporting structure when not secured thereto.

In yet another aspect, the present invention is directed to a scaffolding structure for mounting to a supporting structure. The scaffolding structure comprises a track having a longitudinal direction and being selectively fixable to the supporting structure, and a frame, the frame being movably mountable to the track so that the frame and the track are movable relative to one another in the longitudinal direction of the track, the frame being movable relative to the supporting structure between a first position wherein the frame is supported by the track and the track is supported by the supporting structure, and a second position wherein the frame is supported by the supporting structure and the track is supported by the frame.

In another aspect, the present invention provides a method of providing worker access to a structure having beams, the method includingteh steps of a) providing a scaffold apparatus having a frame supporting a worker platform and a coupling mechanism for coupling the frame to the beam, the coupling mechanism including a track displaceable relative to the frame; b) fixing the track to the beam along a first selected beam segment; c) advancing the frame along the track to adjust the position of the platform to facilitate worker access to parts of the structure generally aligned with the selected beam segment; d) fixing the frame to the beam with the track clear of the beam; e) advancing the track relative to the beam to a second selected beam segment adjacent the first selected beam segment; and f) repeating step c) for the second selected beam segment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a bridge having an embodiment of a scaffolding structure according to the present invention positioned thereon;

FIG. 2 is an end view of a bridge having an embodiment of a scaffolding structure according to the present invention positioned thereon;

FIG. 3 is an end cross sectional view of an aspect of a first embodiment of a scaffolding structure according to the present invention positioned on a bridge, with the scaffolding structure shown in a first position;

FIG. 4 is an end cross sectional view of an aspect of a first embodiment of a scaffolding structure according to the present invention positioned on a bridge, with the scaffolding structure shown in a second position;

FIG. 5 a is a side view of a portion of a bridge having an embodiment of a scaffolding structure according to the present invention positioned thereon, with the scaffolding structure shown in a first position at a first longitudinal location on the bridge;

FIG. 5 b is a side view of a portion of a bridge having an embodiment of a scaffolding structure according to the present invention positioned thereon, with the scaffolding structure shown in a first position at a second longitudinal location on the bridge;

FIG. 5 c is a side view of a portion of a bridge having an embodiment of a scaffolding structure according to the present invention positioned thereon, with the scaffolding structure shown in a second position at the second longitudinal location on the bridge;

FIG. 5 d is a side view of a portion of a bridge having an embodiment of a scaffolding structure according to the present invention positioned thereon, with the scaffolding structure shown in a second position at the second longitudinal location on the bridge;

FIG. 5 e is a side view of a portion of a bridge having an embodiment of a scaffolding structure according to the present invention positioned thereon, with the scaffolding structure shown in a first position at the second longitudinal location on the bridge;

FIG. 6 is an end cross sectional view of an aspect of a second embodiment of a scaffolding structure according to the present invention, with the scaffolding structure shown in a first position;

FIG. 7 is an end cross sectional view of an aspect of a third embodiment of a scaffolding structure according to the present invention positioned on a bridge, with the scaffolding structure shown in a first position;

FIG. 8 is an end cross sectional view of an aspect of a third embodiment of a scaffolding structure according to the present invention positioned on a bridge, with the scaffolding structure shown in a second position.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1 and 2, a portion of a structure 10 is shown. The structure 10 can be in the form of a bridge, and can have a framework including support columns 12, lower longitudinal beams 14, upper longitudinal beams 16, vertical posts 18, and reinforcing struts 20. Referring specifically to FIG. 2, the bridge 10 also includes upper and lower transverse beams 22, and additional cross struts 24. A road surface 26 is supported on the lower longitudinal beams 14 and transverse beams 22. One skilled in the art will appreciate that the bridge 10 is exemplary only, and is described herein solely for the purposes of providing a detailed description of a preferred embodiment of the present invention. Accordingly, it will be appreciated that the present invention may be used with any suitable type of structure or bridge. The bridge 10 serves as a supporting structure for a scaffolding apparatus according to the present invention.

Still referring to FIGS. 1 and 2, a scaffolding apparatus according to one embodiment of the present invention is shown generally at 100. In the particular embodiment shown, the scaffolding apparatus 100 comprises a frame 102 having two side supports 104 and a cross member 106. A platform or basket (also called a spider) 108 can be suspended from the cross member 106 by means of cables 110. The platform 108 can support workers to carry out maintenance on the bridge 10. As can be seen best in FIG. 2, the cross member 106 preferably extends beyond the side supports 104 to facilitate maintenance of exterior portions of the bridge 10. Thus, the spider 108 can be suspended on either the outside or the inside of the bridge, depending on the particular maintenance work being done.

As shown in FIG. 1, the side supports 104 are, in the illustrated embodiment, generally in the form of an A-frame having diagonally downwardly extending legs. A coupling mechanism 112 is provided at the lower end of each leg of the of the side supports 104 for coupling the frame 102 to the beam 16 of the bridge 10. The coupling mechanisms 112 are also generally referred to as feet 112 herein. The coupling mechanism 112 includes a track 111 and actuators 115, described in greater detail subsequently herein.

It can be seen that one advantage of the configuration used in accordance with the present invention is that maintenance operations can be carried out without obstructing vehicle traffic across the bridge 10. Even when the spider 108 must be positioned inside the bridge and close to the road surface 26, such operations can be performed during periods of low traffic, and the spider 108 can be temporarily raised out of the way when a vehicle approaches. The scaffolding structure 100 may be lifted into an initial placement atop the bridge 10 by a mobile crane positioned temporarily on the road surface 26. The spider 108 can be lowered to the level of the road surface to provide for entry and exit of the crew.

As can be seen in FIG. 1, the bridge 10 has a longitudinal direction A. The beams 16 and the track 111 have longitudinal axes that are, when the scaffolding apparatus 100 is supported on the bridge 10, generally parallel to the longitudinal direction A. As described in greater detail subsequently herein, when the track 111 and the frame 102 are coupled together and to the beam 16 in accordance with the present invention, the frame 102 and the track 111 are movable relative to one another in the longitudinal direction of the track 111. The track 111 can include two transversely spaced rail assemblies 114 along which the frame 102 can be displaced.

Now referring to FIGS. 3 and 4, one preferred embodiment of the coupling mechanism 112 for coupling the scaffold apparatus 100 to the beams 16 is shown in greater detail. The coupling mechanism 112 provides an interconnection between the frame 102, rail assemblies 114, and the beams 16. In the embodiment shown, the upper horizontal beam 16 is in the form of an I-beam having a vertical portion (or web) 116, an upper horizontal (flange) portion 118, and a lower horizontal (flange) portion 120. Portions of the bridge 10 other than the upper horizontal beam 16 have been omitted for clarity in some Figures.

In a preferred embodiment, each rail assembly 114 includes a lower track plate (also called bearing plate) 122 and a housing (also called retainer channel) 124. The track plate 122 can include a vertically protruding guide 123 running along its length. In the particular embodiment shown, the housing 124 includes side plates 126 extending upwardly from transversely opposed sides of the bearing plate 122, and top plates 128 directed inwardly and extending towards each other from respective upper ends of the side plates.

The two top plates 128 are vertically spaced apart from the bearing plate 122 to define a retaining channel height 129 (FIG. 3). The top plates 128 have inner edges 128 a that are spaced laterally apart to define an elongated slot 130 that extends along the length of the rail assembly 114. The opposing surfaces of the top plates 128 and bearing plate 122 define upper and lower channel surfaces 125 and 127, respectively.

Fastening brackets 132 can be disposed on the lower track plate 122 to facilitate fixing the rail assembly 114 to the upper horizontal beam 16. For example, in FIG. 3 the rail assembly 114 is fastened to the upper horizontal beam 16 by means of a cable 134 wrapped around the beam 16 and connected at either end to the brackets 132. Alternatively (not shown), the upper horizontal beam 16 and the rail assembly 14 can be provided with respective ones of a pair of engagement elements adapted to interengage for fixing the rail assembly to the beam. The track plate 122 and housing 124 can be made from any suitable material, for example steel or aluminum.

The foot 112 can include a main support leg 140 that, in the embodiment shown, forms a contiguous part of the A-frame side support 104. An axle 142 is rotatably mounted at the end of the main support 140, and wheels (also referred to as rollers) 144 are fixedly mounted to the axle 142. Thus, the wheels 144 can rotate relative to the main support 140 about an axis that is, in the illustrated embodiment, fixed relative to the frame 102. One skilled in the art will realize that the axle 142 could be fixedly mounted to the support leg 140, and the wheels 144 rotatably mounted to the axle 142, without affecting the operation of the present invention. Similarly, both the axle 142 and wheels 144 could be rotatably mounted. The rollers 144 have a diameter 145 that is less than the channel height 129. The difference between the roller diameter 145 and the channel height 129 defines a channel clearance 147.

When the frame 102 and track assembly 111 are mounted to one another, the wheels 144 fit within and are surrounded by the housing 124 of the rail assembly 114, as shown in FIGS. 3 and 4. The main support leg 140 projects generally upwardly through the elongated slot 130. The guide 123 assists in maintaining alignment of the wheels 144 within the housing 124. Once the wheeled portion of the foot 112 is positioned within the rail assembly 114, the ends of the rail assembly are preferably sealed by an end plate (not shown) to prevent the foot 112 from moving beyond the ends of the rail assemblies 114.

The foot 112 includes actuators 115 as mentioned previously. The actuators 115 can generally include a body portion and an extension portion that is movable relative to the body portion for moving the frame 102 relative to the beam 16 when in use. The actuators 115 can be in the form of jacks 150, having body portions 156 secured to the frame 102, and extension portions 158 telescopically housed within the body portions 156.

The jacks can be hydraulic actuators, the body portions 156 providing a cylinder or chamber and the extension portion 158 including a piston slidable within the chamber 156. The chamber 156 can be fixed to the frame 102, and in the illustrated embodiment, is secured to the main support leg 140 of the frame 102 by means of struts 152 and additional reinforcing members 154.

Alternatively, one or more of the jacks 150 can be, for example, but not limited to, pneumatic actuators, or mechanical screw-type jacks. In the particular embodiment shown, the extension members 158 include a rod member 160 slidable within the chamber 156, and an engagement member 162 fixed to the rod member 160 and adapted to engage a portion of the beam 16. In the embodiment illustrated, the rod member is oriented generally vertically, and the engagement member 162 extends laterally inwardly for engaging an upper surface of the lower flange 120 of the beam 16. Each foot 112 can include one or more jacks 150. In the embodiment illustrated, each foot 112 is provided with four jacks 150.

The coupling mechanism 112 of the present invention is movable between first and second positions. The first position corresponds to a state in which the rails 114 of the track 111 are fixed relative to the beam 16 (i.e. held stationary), and the frame 102 is displaceable relative to the rails for advancing the platform 108 therealong. The second position corresponds to a state in which the frame is fixed relative to the beam 16 (i.e. held stationary), and the rails 114 of the track 111 are displaceable relative to the frame 102 for advancing the track 111 relative to the beam 16. In general terms, this allows a relatively short length of track 111 to be “walked” along the relatively longer length of beam 16. Between “steps” (i.e. between repositioning of the track 111), workers occupying the platform 108 can carry out the required work and reposition the platform 108 along the stationary track 111 as required.

Further details of the operation of one embodiment of the scaffolding apparatus 100 according to the present invention will now be described.

FIG. 3 shows a coupling mechanism 112 in the first position. The track 111, and in particular the lower track plate 122, rests on the upper horizontal portion 118 of the I-beam 16 along a selected segment of the length thereof. The weight of frame 102 bears against the rail assembly 114, so that the track can be fastened securely to the upper horizontal beam 16 by cable 134. Thus, the rail assembly 114 will be fixed relative to the upper horizontal beam 16, and therefore also relative to the bridge 10.

The jacks 150 are in a retracted position, so that the engaging members 158, and in particular the horizontal portions 162 thereof, do not contact the lower horizontal portion 120 of the upper horizontal beam 16. The weight of the frame 102 is supported, by way of main support leg 140, on the wheels 144, which rest on the lower channel surface 125. In this configuration, therefore, the frame 102 is supported by the rail assemblies 114, and the rail assemblies 114 are in turn supported by the bridge 10. When work is being carried out, the frame 102 can be course be fixed relative to the rail assemblies 114 and bridge 10. For this purpose, the horizontal portions 162 of the engaging members 162 can be provided with vice members (also called clamping elements) 164 that can be moved inwardly to contact and apply pressure to the vertical portion 116 of the upper horizontal beam 16 so as to fix the frame 102 in position. When it is desired to advance the frame 102 along the rail assemblies 114, the vice members 164 may be retracted. The vice members 164 may be mechanical, hydraulic or pneumatic in the embodiment illustrated, the vice members 164 are mechanical and are of the screw type, as shown in FIGS. 3 and 4.

When the vice members 116 have been retracted, the frame 102 will be movable relative to the rail assemblies 114 and the bridge 10 in the longitudinal direction of the bridge 10. Thus, by way of the wheels 144 rolling along the lower channel surface 127, the frame 102 can advance along the rail assemblies 114 until it reaches the ends thereof. The ends are preferably capped to prevent inadvertent overtravel of the rollers 144 out of the channel 124, and to keep the rail assemblies 114 and frame 102 unreleasably coupled together.

Once the frame 102 has reached the ends of the rail assemblies 114, the rail assembly can be shuttled into position along a subsequent selected segment of the length of the beam 16 in accordance with the present invention. This can be performed by moving the coupling apparatus into the second position. Prior to doing so, the cables 134 (if used) can be removed from the rail assemblies 114. Also, for safety reasons, the spider 108 can be moved to an elevated position near to or immediately below the cross member 106.

FIG. 4 shows the relative locations of the coupling apparatus 112, rail assembly 114 and upper horizontal beam 16 when the coupling apparatus 102 is in the second position. When the frame 102 is in the second position, the jacks 150 are extended so that the engaging members 158, and in particular the horizontal portions 162 thereof, contact the lower horizontal portion 120 of the upper horizontal beam 16. This raises the leg 140, and therefore the frame 102, into an elevated position relative to the upper horizontal beam 16 and therefore also relative to the bridge 10.

As the leg 140 is raised by the jacks 150, the wheels 144 are raised off the lower channel surface 127 and contact the upper channel surface 125 of the roller retaining channel 124. As the leg 140 continues to be lifted upward by the jacks 150, the rail assembly 114 will be lifted off the upper horizontal portion 118 of the upper horizontal beam 16 so that it is supported by (i.e. suspended from) the wheels 144. Thus, the frame 102 is supported by the bridge 10 (by way of the jacks 150 engaging the upper horizontal beam 16) and the rail assemblies 114 are supported by the frame 102 (by way of the wheels 144). Furthermore, because of the weight of the frame 102 and the frictional forces acting between the engagement members 158 and the lower horizontal portion 120 of the upper horizontal beam 16, the frame 102 will be fixed relative to the bridge 10. To further fix the frame 102 relative to the bridge 10, once the jacks 150 have fully extended, the vice members 164 can again be brought into contact with the vertical web 116 of the upper horizontal beam 16. The rail assemblies 114 are movable relative to the frame 102 (and therefore relative to the bridge 10) in the longitudinal direction of the bridge 10. In particular, the wheels 144 act as rollers to allow the rail assemblies 114 to be moved relative to the frame 102 and bridge 10.

Once the rail assemblies have been advanced into position along a new segment of the beam 16, the jacks 150 can be retracted so that the frame 102 (and therefore the rail assemblies 114) are lowered. Once the rail assemblies 114 have been lowered into contact with the upper horizontal beam 16 in their new position, they can be refastened to the upper horizontal beam 16 by way of the cables 134.

Now referring to FIGS. 5 a through 5 e, the operational sequence of a maintenance operation, using an embodiment of the scaffolding structure 100 according to the present invention, is shown. In FIGS. 5 a to 5 e, certain features, such as the spider 108 and portions of the bridge 10, have been omitted for the sake of clarity. In FIGS. 5 a to 5 e, the longitudinal direction A is the same as the longitudinal direction A of the bridge 10 shown in FIG. 1.

Referring first to FIG. 5 a, the frame 102 is in the first position, corresponding to that shown in FIG. 3. Specifically, the frame is supported by the rail assemblies 114, and the rail assemblies 114 are supported by the upper horizontal beam 16. By rolling engagement of the rollers 144 along the lower channel surface 127 (FIG. 3), the frame 102 can be advanced along the rail assemblies 114 in the longitudinal direction A until it reaches an end 136 of the rail assemblies 114, as shown in FIG. 5 b.

With reference now to FIG. 5 c, once the frame 102 has reached the end of the rail assemblies 114, the cables 134 can be unfastened and the coupling mechanism 112 can be moved into the second position as shown in FIG. 4. Specifically, the jacks 150 (FIG. 4) are extended so that the frame 102 and rail assemblies 104 are elevated relative to the upper horizontal beam 16, and the rail assemblies 114 are suspended from the wheels 144 (FIG. 4).

In this position (second position of the coupling mechanism), the rail assemblies 114 are clear of the upper horizontal beam 16, so that they can be rolled in the longitudinal direction A along the wheels 144 (FIG. 4) to their new position, as shown in FIG. 5d.

Once the rail assemblies 114 are in their new position, the coupling mechanism can moved into the first position (FIG. 3), so that the rail assemblies 114 again rest on the upper horizontal beam 16, with the frame 102 resting on the rail assemblies 114 as shown in FIG. 5 e. The cables 134 can then be refastened, and the frame 102 can then be advanced along the (repositioned) rail assemblies 114. By repeating the above process, the frame 102 can be advanced along the entire length of the bridge 10 without the need to lay down or pick up any additional track members to support the frame 102.

In one embodiment, small hand winches may be used to advance the frame 102 along the rail assemblies 114 (when the frame 102 is in the first position) and the rail assemblies 114 along the frame 102 (when the frame 102 is in the second position). These winches can be used to lock the frame into a particular working position as a safety measure. Alternatively, the wheels 144 may be motorized. In addition to vice members 164, clamps may be provided for locking the frame 102 in position relative to the rail assemblies 114, to prevent accidental movement of the frame 102 during a maintenance operation.

One skilled in the art will appreciate that the design of the housing 124 and foot 112 described above are merely one embodiment of the present invention, and that many variations are possible without departing from the scope of the present invention. For example, with reference to FIG. 6, alternate feet 212 and rail assemblies 214 could be used. Rail assemblies 214 comprise a generally circular housing 216, with a flattened bottom portion 218 for resting on the upper horizontal beam 16 of the bridge 10, rather than the square of the rail assemblies 114. The foot 212 has a shape corresponding to the rail assemblies 214, and a plurality of bearings 220 are disposed in the foot 212 to permit smooth longitudinal movement of the foot 212 and the rail assemblies 214 relative to one another.

It is also within the contemplation of the inventor that the jacks 150 may be adapted for use with a bridge 10 in which the upper horizontal beam 16 is of a type other than an I-beam. With reference now to FIGS. 7 and 8, such alternate embodiments are described. In these alternate embodiments, identical reference numerals have been used to those used in FIGS. 3 and 4, with the letter “a” denoting the alternate embodiment. Thus, the jacks are denoted by 150 a, the housing is denoted by 124 a, and so on.

In FIGS. 7 and 8, the upper horizontal beam 16 a is a box member rather than an I-beam, and alternate embodiments of a foot 112 a and rail assembly 114 a are shown. In these alternate embodiments, the jacks 150 a are positioned to engage the upper surface of the upper horizontal portion 118 a of the box beam 16 a. Although not visible in FIGS. 7 and 8, cutouts are provided in the outside edges of the track plate 122 a to accommodate the horizontal portions 162 a of the engaging members 158 a of the jacks 150 a. Thus, in the first position shown in FIG. 7, the jacks 150 a are in the retracted position, and the horizontal portions 162 a of the engaging members 158 a are positioned above both the upper horizontal portion 118 a of the upper horizontal beam 16 a, and also above the track plate 122 a. The vice members 164 a contact and apply pressure to the outside of the side plates 126 a to fix the frame 102 a in position during a maintenance operation. When the vice members 164 a are retracted, the frame 102 a can move relative to the rail assemblies 114 a by way of the wheels 144 a rolling along the track plate 122 a.

When the frame 102 a has advanced to the end of the rail assemblies 114 a, the horizontal portions 162 a of the engaging members 158 a will be aligned with the cutouts (not shown) in the track plate 122 a. Thus, as shown in FIG. 8, the jacks 150 a are then moved into the extended position, causing the horizontal portions 162 a to engage the upper surface of the upper horizontal portion 118 a of the upper horizontal beam 16 a. As the jacks 150 a continue to extend, the frame 102 a will be raised into the position shown in FIG. 8, with the rail assembly 114 a suspended from the frame 102 a (by way of the top plates 128 a resting on the wheels 144 a. This permits the rail assemblies 114 a to move relative to the frame 102 a and the bridge 10 by means of the rail assemblies 114 a rolling along the wheels 144 a.

In one embodiment, a flexible hood connected to a vacuum source may be used to contain and remove dust and debris resulting from maintenance operations. Other tools and equipment can also be used with the present invention. For example, an overhead canopy can be positioned above the road surface 26, mounted on wheeled platforms on the sides of the roadway, to follow beneath the scaffolding structure 100 and capture debris. Catwalks can also be provided on the scaffolding structure if desired.

While the embodiments described above have been directed toward use with a bridge having substantially linear upper horizontal beams, it is also envisioned that the present invention may be modified by adapting the rail assemblies and frame for use with a bridge having curved upper horizontal beams. For example, a rail assembly comprising a plurality of flexibly connected segments could be used, permitting the rail assembly to adapt to the curvilinear shape of the particular upper horizontal beam upon which it rests. Furthermore, the engaging members of the jacks could be adapted to apply vice-like inward pressure to the sides of the upper horizontal beams to maintain the frame in place when the frame is in the raised position.

It will be appreciated by one skilled in the art that numerous other variations and modifications may be made to the embodiments described above without departing from the scope of the present invention. All such variations and modifications are intended to be encompassed within the scope of the present invention as defined by the appended claims. 

1. A scaffolding apparatus providing access to a structure, comprising: a frame, the frame comprising two side supports and a cross-member connected between the side supports, the frame supporting a worker platorm; at least one coupling mechanism coupled to each side support for coupling the frame to a supporting structure; each coupling mechanism including a rail assembly, each rail assembly extending in a longitudinal direction and being selectively securable to the supporting structure, rail assembly having a housing shaped to retain a roller member secured to the frame therewithin and to permit movement of the track and the at least one foot relative to one another in the longitudinal direction of the supporting structure; an actuator secured to the frame and adapted to selectively move the coupling mechanism between a first position wherein the frame is movable relative to the rail assembly and the supporting structure in the longitudinal direction, and a second position wherein the frame is fixed relative to the supporting structure and the rail assemblies are movable relative to the frame and the supporting structure in the longitudinal direction.
 2. The scaffolding structure of claim 1, wherein the first position defines a lowered position in which each rail assembly bears against the support structure, and the weight of the frame bears against each rail assembly, and wherein the second position defines a raised position in which each rail assembly is raised clear of the support structure, and the weight of the frame bears against the support structure.
 3. The scaffolding structure of claim 2, wherein each coupling mechanism comprises at least one jack, the jacks adapted to engage the supporting structure and elevate the frame to move the coupling mechanism from the first position to the second position.
 4. The scaffolding structure of claim 3, wherein each housing defines a roller retaining channel having a lower channel surface for bearing against the roller member when the coupling mechanism is in the first position.
 5. The scaffolding structure of claim 4, wherein each retaining chamber has an upper channel surface for bearing against the roller member when the frame is in the second position.
 6. A scaffolding structure comprising: a frame; a track, the track being selectively fixable to a supporting structure having a longitudinal direction, the track being movably mountable to the frame; a mechanism secured to the frame and adapted to selectively move the frame between a first position wherein the frame is movable relative to the track and the supporting structure in the longitudinal direction of the supporting structure, and a second position wherein the frame is fixed relative to the supporting structure and the track is movable relative to the frame and the supporting structure in the longitudinal direction of the supporting structure when not secured thereto.
 7. The scaffolding structure of claim 6, wherein the first position is a non-elevated position relative to the supporting structure, and wherein the second position is an elevated position relative to the supporting structure.
 8. The scaffolding structure of claim 7, wherein the mechanism comprises a plurality of jacks, and wherein the jacks are adapted to engage the supporting structure and elevate the frame into the second position.
 9. The scaffolding structure of claim 8, wherein the frame comprises at least one foot, and wherein the track comprises at least one rail assembly, and wherein each at least one rail assembly comprises a housing shaped to receive and movably retain therewithin a corresponding at least one foot.
 10. The scaffolding structure of claim 9, wherein each housing has an interior surface or surfaces, and wherein each at least one foot comprises a member or members for rollably engaging the interior surface or surfaces of the corresponding housing within which the foot is retained.
 11. The scaffolding structure of claim 10, wherein each housing has an upper interior surface and a lower interior surface, and wherein each foot comprises a wheel or wheels, and wherein when the frame is in the first position, the wheel or wheels support the frame and are rollably disposed on the lower interior surface of the corresponding housing, and wherein when the frame is in the second position, each at least one rail assembly is supported by its upper interior surface, the upper interior surface resting rollably on the wheel or wheels of the corresponding foot.
 12. A displaceable scaffolding apparatus, comprising: a) a frame supporting a worker platform; b) a coupling mechanism connected to the frame for coupling the frame to a pair of beams of a structure, the coupling mechanism movable between a first position and a second position; c) the coupling mechanism including a track fixable relative to the beams and along which the frame can be advanced when the coupling mechanism is in the first position; d) the frame being fixable relative to the beams for advancing the track relative to the frame when the coupling mechanism is in the second position.
 13. The apparatus of claim 12 wherein the coupling mechanism comprises actuators for moving the coupling mechanism between the first and second positions, the actuators having a body portion fixed to the frame and an extension portion displaceable relative to the body portion and adapted to engage the beam.
 14. The apparatus of claim 13 wherein the track is raised clear of the beam when the coupling mechanism is in the second position.
 15. The apparatus of claim 14 wherein the coupling mechanism comprises a plurality of rollers rotatable about a roller axis, the roller axis being fixed relative to the frame, and the rollers being coupled to the track.
 16. The apparatus of claim 15 wherein the track comprises rail elements having a roller retaining channel along which the rollers travel for coupling the frame to the track, the roller retaining channel having a channel height that extends between a lower channel surface and an upper channel surface.
 17. The apparatus of claim 16 wherein the channel height is greater than the roller diameter by an amount defining a channel clearance, and wherein the rollers engage the lower channel surface when the coupling mechanism is in the first position, and engage the upper channel surface when the coupling mechanism is in the second position.
 18. The apparatus of claim 17 wherein the total displacement of the extension portion when moving the coupling mechanism between the first and second positions is greater than channel clearance.
 19. A method of providing worker access to a structure having beams, comprising: a) providing a scaffold apparatus having a frame supporting a worker platform and a coupling mechanism for coupling the frame to the beam, the coupling mechanism including a track displaceable relative to the frame; b) fixing the track to the beam along a first selected beam segment; c) advancing the frame along the track to adjust the position of the platform to facilitate worker access to parts of the structure generally aligned with the selected beam segment; d) fixing the frame to the beam with the track clear of the beam; e) advancing the track relative to the beam to a second selected beam segment adjacent the first selected beam segment; and f) repeating step c) for the second selected beam segment.
 20. The method of claim 19 wherein the coupling mechanism includes actuators movable between advanced and retracted positions, and wherein step d) includes moving the actuator to the advanced position. 